The present invention is related to Japanese patent application No. Hei. 11-109208, filed Apr. 16, 1999; No. 2000-50946, filed Feb. 28, 2000; the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates generally to a fuel injection pump for internal combustion engines, and more particularly to a fuel injection pump for internal combustion engines which reduces pump damage during overrunning of the internal combustion engine.
2. Background of the Invention
As disclosed in Japanese Patent Laid-Open No. 249134/1994, a fuel injection pump is known in which a driving force transmission member (cam ring), mounted eccentrically on a drive shaft, is moved orbitally corresponding to rotation of the drive shaft. The transmission member drives reciprocating plungers, arranged at equi-angular intervals circumferentially around the drive shaft. By this action, the plungers pressurize fuel that has been sucked into pressurization chambers.
An example the fuel injection pump, described above, is shown in FIG. 4. Here, a fuel injection pump 100 is shown as a radial pump in which fuel sucked into fuel pressurization chamber 106 is pressurized by reciprocating movements of plungers 102. In the fuel pump of FIG. 4, plungers 102 are typically arranged at intervals of 120xc2x0 around a drive shaft 110. However, in FIG. 4, two of the three plungers 102 are omitted, leaving only one plunger shown.
The plunger 102 is supported in a cylinder 101 so that plunger 102 can be reciprocated freely. A tappet 103 slides on cam ring 112 fitted slidably around an outer circumference of a cam 113. A lower seat 104 receives an urging force from spring 105 urging plunger 102 and tappet 103 toward cam ring 112. The plunger 102, tappet 103 and lower seat 104 constitute a movable unit.
When an internal combustion engine (hereinafter engine) overruns due to abnormal combustion, drive shaft 110 overruns, causing an increase in speed of reciprocating movement of the movable unit. This causes an inertial force in the lifting direction of the movable unit to become larger than the urging force of spring 105. As a result, the tappet 103 leaves the cam ring 112.
When the tappet 103 leaves the cam ring 112, the plunger 102 travels beyond top dead center. As a result, the quantity of fuel discharged from the fuel injection pump 100 is not controlled with a high accuracy. Moreover, the elements of the movable unit can be damaged due to impact of the tappet 103, which leaves the cam ring 112, with cam ring 112. The present invention was developed in light of these drawbacks.
It is therefore an object of the present invention to provide a fuel injection pump adapted to stop the supply of fuel when a movable member for pressurizing the fuel is lifted beyond a top dead center and leaves a respective driving force transmission member.
It is another object of the present invention to keep the movable member, which has left the driving force transmission member, from colliding with the transmission member and thereby causing damage.
To accomplish these and other object of the present invention, a fuel injection pump is provided having a device for regulating reciprocating movements of the movable member when the movable member is lifted beyond top dead center. Such a fuel injection pump comprises a movable member adapted to pressurize fuel sucked into a fuel pressurization chamber. The movable member has at least a first outside diameter portion and a second outside diameter portion. A support is provided having a first bore diameter portion and a second bore diameter portion. The first bore diameter portion is slidingly engaged with the first outside diameter portion to support the movable member. A cam is mounted on and rotated with a drive shaft.
A driving force transmission member is provided between the cam and a first end of the movable member. An urging device is positioned between at least a portion of the movable member and the support. The urging device urges the movable member toward the driving force transmission member. As such, the cam, the driving force transmission member and the urging device drive the movable member in a reciprocating fashion corresponding to rotation of the cam to pressurize the fuel. Also, the second bore diameter portion has an inside diameter slightly larger than an outside diameter of the second outside diameter portion, the second outside diameter portion is positioned proximate the cam with respect to second bore diameter portion, wherein the outside diameter of the second outside diameter portion creates an interference fit with the second bore diameter portion when the movable member is lifted beyond a top dead center position. Therefore, when an engine overruns, causing the movable member to be lifted beyond top dead center, the reciprocating movements of the movable member are regulated, and fuel discharge is stopped. Moreover, since the collision of the movable member with the driving force transmission member is prevented, damage to the fuel injection pump is prevented.
In another aspect of the invention, a cam ring, mounted slidably on an outer circumference of a cam, is slidingly mounted on the movable member. As such, the cam ring moves corresponding to the rotation of the drive shaft, and thereby drives the movable member reciprocating fashion, thereby constituting the above-mentioned driving force transmission member.
According to yet another aspect of the invention, a plunger or a connecting member in the fuel injection pump is press fitted into a cylinder when the movable member is lifted beyond. the top dead center. As such, the reciprocating movements of the movable member are regulated. This enables the reciprocating movements of the plunger to be regulated by a simple structure without requiring a new member for regulating the reciprocating movements of the movable member.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.